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KVM: vmx: do not unconditionally clear EFER switching

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Do not unconditionally call clear_atomic_switch_msr() when updating
EFER.  This adds up to four unnecessary VMWrites in the case where
guest_efer != host_efer, e.g. if the load_on_{entry,exit} bits were
already set.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2018-09-26 09:23:43 -07:00 committed by Paolo Bonzini
parent b7031fd40f
commit 02343cf207
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kvm/vmx.c
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@ -2790,8 +2790,6 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
ignore_bits &= ~(u64)EFER_SCE;
#endif
clear_atomic_switch_msr(vmx, MSR_EFER);
/*
* On EPT, we can't emulate NX, so we must switch EFER atomically.
* On CPUs that support "load IA32_EFER", always switch EFER
@ -2804,8 +2802,12 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
if (guest_efer != host_efer)
add_atomic_switch_msr(vmx, MSR_EFER,
guest_efer, host_efer, false);
else
clear_atomic_switch_msr(vmx, MSR_EFER);
return false;
} else {
clear_atomic_switch_msr(vmx, MSR_EFER);
guest_efer &= ~ignore_bits;
guest_efer |= host_efer & ignore_bits;